信江盆地晚白垩世塘边组沉积特征与古气候研究

发布时间：2018-03-01 02:11

  本文关键词： 信江盆地 晚白垩世 物源分析 古大气CO_2浓度　出处：《东华理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：信江盆地位于赣杭构造带中部,是中国东南部地壳拉张背景下形成的陆相断陷盆地之一。白垩系陆相红层发育,是区内丹霞地貌发育的物质基础。本次通过野外露头测量和描述、砾石统计、砂岩薄片鉴定及碎屑颗粒统计、古土壤碳-氧同位素分析,对晚白垩世塘边组沉积特征、物源和古气候进行了详细的研究,取得了以下研究成果:信江盆地塘边组为河流-湖泊-风成沉积。塘边组早期发育辫状河沉积的河床亚相和泛滥平原亚相,中期发育湖泊沉积的滨湖和浅湖亚相,晚期气候干旱化,转变为风成相。早期沉积的砾岩层砾石成分复杂,分选磨圆差,成分和结构成熟度低。古流向玫瑰花图指示物源来自盆地的北、北东、东部和南部。砂岩碎屑颗粒统计表明,石英含量高,岩屑次之,长石最少。C_m=3.72,指示成分成熟度为中等,分选、磨圆为中等偏好,指示中等结构成熟度。通过Dickinson投图可知,砂岩碎屑沉积物主要来自再旋回造山带物源区,消减杂岩带提供了大量的物源,同时具有弧造山带物源的成分。盆地两侧隆起地区的中-新元古界低级变质岩系地层、燕山期中酸性火山-侵入杂岩和塘边组沉积时期遭受剥蚀的前晚白垩世地层可能也提供了碎屑物源。对采自江西信江盆地晚白垩世塘边组的成壤碳酸盐样品碳、氧同位素测试表明,δ~(13)C值在-4.30‰~-2.10‰之间,平均值为-2.84‰。δ18O值在-6.62‰~-1.14‰之间,平均值为-3.62‰。由Cerling经验公式估算出晚白垩世Campanian期75Ma的大气CO_2浓度在782~1420 ppmv之间,平均值为1181ppmv,是当今大气CO_2浓度的2~4倍左右。因此,基于信江盆地塘边组成壤碳酸盐的大气CO_2浓度估算结果,可能指示了晚白垩世Campanian晚期存在一个大气CO_2浓度高值,反映了晚白垩世大气CO_2浓度的波动性。
[Abstract]:The Xinjiang basin, located in the middle of the Ganhang tectonic belt, is one of the continental faulted basins formed in the crustal extensional background of southeastern China. It is the material foundation of Danxia geomorphology development in this area. Through field outcrop survey and description, gravel statistics, sandstone sheet identification and clastic particle statistics, paleosol carbon-oxygen isotope analysis, the sedimentary characteristics of the late Cretaceous Tangbian formation were studied. The provenance and paleoclimate were studied in detail, and the following results were obtained: the Tangbian formation in Xinjiang Basin was fluvial, lacustrine and aeolian sediments, and the fluvial bed subfacies and flood plain subfacies were developed in the early stage of the Tangbian formation. The lacustrine and shallow lacustrine subfacies were developed in the middle period, and the late climate was arid and changed into eolian facies. The trace indicator of the paleoflow rose map comes from the north, north, east, east and south of the basin. According to the statistics of sandstone clastic grains, quartz content is high, lithic debris is the second, feldspar is the least. Sorting, grinding circle is medium preference, indicating medium structural maturity. According to the Dickinson chart, sandstone-clastic sediments mainly come from the source area of the re-cycle orogenic belt, and the subtractive complex belt provides a large number of provenances. The lower metamorphic strata of the Mesoproterozoic in the uplift areas on both sides of the basin, The acid volcanic-intrusive complex in Yanshanian period and the denuded strata of Tangbian formation in the sedimentary period may also provide a source of clastic material. The carbonates collected from the late Cretaceous Tangbian formation in Xinjiang Basin, Jiangxi Province, were studied. The oxygen isotope test shows that the 未 ~ (13) C value is -4.30 鈥，

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